Method of open hearth furnace operation



Aprf El?? @341 F. E. LEM-w METHOD OF OPEN HEARTH FURNACE OPERATION FiledSept. 16, 1929 2 Sheefcs-Sheet l JKM WITNESS pl' il?, 3934-. F, E LEAHY3,955,58@

METHOD 0F OPEN HEARTH FURNACE OPERATION lFiled Sept. 16, 1929 2Sheets-Sheet 2 WITNESS Patented Apr. 17, 1934 UNITED STATES PATENTOFFICE METHOD OF OPEN HEARTH FURNACE OPERATION Application September 16,1929, Serial No. 392,769

12 Claims.

The present invention is designed to enhance rapidity of production ofopen hearth steel without unduly decreasing the normal life of thefurnace.

Among the principal objects of the invention, therefore, is theprovision of a method of furnace operation which, without increasing thenormal rate of deterioration of the furnace, is effective in reducingthe time required for the heat treatment of the metal, with the resultthat by the use of the said method of materially greater amount of steelcan be produced during the operative life of the furnace than hasheretofore been possible because of the lessened time required for eachheat while, on the other hand, the furnace may be maintained inoperative condition for a period at least as long, and frequentlylonger, than substantially similar furnaces when operated in accordancewith the best practice heretofore employed.

My invention is therefore advantageous in that, among other things, itreduces the ultimate cost of the steel by enhancing the amount thereofwhich can be produced during the .operative life of the furnace wherebythe proportion of the cost of furnace replacement and operating costswhich must be allocated against each ton of the finished product iscorrespondingly reduced.

My invention is further advantageous in that its employment tends toreduce or substantially eliminate the foaming of the charge during therening period and which, when present, is inimical to the satisfactoryand economical production of open hearth steel.

Other objects, advantages and novel steps and features comprehended bymy invention are hereinafter more specifically mentioned or will beapparent to those skilled in the art from the following description ofone manner of performing it in connection with which reference may behad to the accompanying drawings.

Heretofore in modern open hearth steel practice it has been customary toutilize throughout the heat treatment of the charge in the furnace anon-luminous or blow torch type of flame derived by burning gas and airmixed prior to combustion for the reason, among others, that a flame ofthis character has the abilityto adequately penetrate that portion ofthe charge which consists of metal scrap and which usually is chargedlast into the furnace and rests in loosely piled condition on thesub-jacent layers of ore, pig iron and limestone which are initiallydisposed at the bottom of the charge. For the production of this type offlame, the air necessary for combustion is usually separately preheatedin whole or in part and then mixed with the gas which is eitherseparately preheated or not, depending upon the kind of gas being used;thus, producer gas is customarily preheated before its mixture with theair while coke oven gas is not. The ensuing combustion of the hotmixture of air and gas results in the production of the saidnon-luminous flame which is of high temperature but of such quality orcharacter that the percentage of heat transference which it is capableof effecting by radiation is at a minimum although the flame is capableof imparting a high degree of heat transference by convection.

The operation of an open hearthfur-nace is divided into two distinctperiods or stages, namely, the melt-down period during which the chargeis being reduced to substantial fluidity, and the subsequent refiningperiod.' during which the melted charge is subjected to the further heattreatment necessary or desirable before it can be tapped. During themelt-down period the charge is highly heat absorptive with the resultthat the greater portion of the heat of the nonluminous flame whichimpinges more or less directly upon the heaped-up scrap and otherportions of the charge is taken up by the latter while the balance ofthe heat of the flame other than that which eventually leaves thefurnace and passes to the stack is absorbed by the furnace walls androof. Therefore, during the meld-down of the charge which ordinarilyrequires about one-half of the total operating time of each heat, anon-luminous, blow torch type of flame can be effectively employed at atemperature sufficient to bring about a very rapid melting of the chargewithout excessive or undue burning of the refractory walls and roof ofthe furnace as the walls and roof, during this period, absorb but arelatively small proportion of the total heat of the flame.

At the conclusion of the melt-down period, however, the metal of thecharge has been reduced to fluid condition and rests in the hearth ofthe furnace overlaid by a thick layer of slag which is of a highlyrefractory nature, derived as it is in large part, from the limestone inthe charge. The flame passing through the furnace is thus in effectinterposed between two refractory juxtaposed surfaces, namely, the slagcovering on the top of the charge and the furnace roof, both of whichare approximately similarly heat-absorptive, and it is well known thatwhen this condition is reached it becomes necessary to materially reducethe temperature of the flame so as to prevent excessively rapid burningout and deterioration of the furnace. But such reduction immediately andnecessarily results in a lessened heat transference to the charge withcon- 5 sequent prolongation of the refining stage beyond that whichwould be required if the temperature of the flame could be maintained atthe same point during the refining period as during the meltdown. Thefurnace operator has therefore hithlC erto been confronted with theproblem of keeping the fiame temperature during the refining period at amaximum commensurate with an economical furnace life and the rate ofproduction has thus been necessarily limited to that point at which thefurnace deterioration becomes so excessive as to increase the cost ofthe product against which it must be charged by an amount which rendersthat product uncommercial.

I have discovered that the length of the refining period may bematerially shortened without a disproportionate increase in the wear andtear on the furnace or, in fact, without any material shortening of itsnormal life by employing different types of flame for the melt-down andfor the refining stages respectively, with the result that I am able toeffect the melting down of the charge as rapidly and with as littlefurnace deterioration as in the best commercial practice heretoforeemployed and to thereafter refine the charge in a much shorter time thanand with at least as little furnace deterioration as has heretofore beenpossible when using a non-luminous or blow torch type of flame for thepurpose as heretofore described.

More specifically, and in accordance with my invention, I employ for themelt-down of the charge a high temperature non-luminous fiame which, asabove described, has the quality of readily penetrating the charge andof reducing it to fluid condition, without appreciable localized heatingand in a minimum of time, and for the subsequent refining of the chargea luminous radiant flame desirably derived from the combustion of aliquid fuel in association with a suitable quantity of air. Among thefuels which may be employed for this purpose are tar, fuel oil, or cokeplant residue, for as these fuels are high in hydrocarbons they areamong the most desirable for obtaining the luminous name, a quality orcharacteristic of which is its ability to effect a transference of alarge proportion of its heat by radiation as distinguished fromconvection. By the use of a flame of this type during the refiningperiod, I am enabled to bring about substantially as great heattransference to the 4-fbath while maintaining the flame at a temperatureinsufficient to unduly deteriorate the furnace as would be possible whenusing a nonluminous flame of the same temperature as that customarilyused during the melt-down period but which, as above pointed out, is sodestructive to the furnace when at such temperature as to renderimpracticable its employment for refining. The radiant, luminous,relatively low temperature flame, however, is capable of satisfactorilyheating the charge during its passage through the furnace in a muchshorter period of time than a non-luminous ame of like temperature andthus of correspondingly shortening the refining period, with the resultthat although the luminous fiame be maintained at a temperature notunduly inimical to the refractories of the furnace, the'refining of thecharge is completed in a much shorter time than has hitherto beenpossible when a non-luminous flame of like temperature is employed forthe purpose, with corresponding increase in the quantity of steel whichcan be produced during the normal life of the furnace.

The practice of my invention is in no way confined to any particularform or type of open hearth furnace nor to the use of any particular orspecific fuels other than those adapted to produce a non-luminous flameduring the meltdown period and a luminous flame during the subsequentrefining of the charge. However, to facilitate comprehension of theinvention by those skilled in the art, I have illustrateddiagrammatically in the accompanying drawings one form of furnace welladapted for the performance of the invention and to which I shall nowbriefly refer, as well as to the manner of practising the invention inconnection with such a furnace arranged by way of example for theemployment of coke oven gas for the melting of the charge and a liquidfuel, such as tar or coke plant residue, for the refining thereof.

Referring now more particularly to the drawings, Fig. 1 is adiagrammatic plan view, partially in elevation and partially inhorizontal section,

vof the furnace and its associated regenerator or checker chambers andother parts, and Fig. 2 is a longitudinal vertical section substantiallyon the line 2-2 in Fig. l, like symbols of reference being used todesignate the same parts in both figures.

'I'he furnace as shown is of substantially standard construction,comprising the usual hearth 1, roof 2, end walls 3 3 and side walls 4 4,the construction of both ends of the furnace and of the parts associatedtherewith being similar in accordance with the usual practice. Thus,disposed laterally of each end of the furnace are a pair of checkerchambers 5, 6 connected by the usual necks 7, 8 with a common slagpocket 9 disposed beneath the adjacent end of the furnace; from thisslag pocket fiues or uptakes l0, 10 extend vertically on either side ofthe center line of the furnace in front of the adjacent end wall 3 toterminate on opposite sides of a central longitudinally extending walll2 colloquially known as the dog house. The uptakes 10, l0 are thuseffective to direct into the furnace at that end thereof from which itis being fired, the major portion of the air required for combustion andwhich has been previously preheated in the adjacent checker chambers.

For supplying the fuel to the furnace a burner generally designated as Bis disposed in a port or tunnel 13 extending longitudinally through thewall l2 and adjacent end wall. 'Ihis burner is desirably of theaspirating type and comprises a tubular body 14 preferably surroundednear its inner end with a water jacket 15 through which water may becirculated by valve controlled pipes 16, and is so arranged that eithergaseous or liquid fuel may be injected into the furnace.

through the burner at will. Thus, as diagrammatically shown, a valvecontrolled gas pipe 17 is arranged to direct gaseous fuel such as cokeoven gas into the funnel-shaped outer end of the burner, while by meansof a pipe 18 extending substantially through the burner and terminatingadjacent its inner end, liquid fuel such as tarA supplied from a valvecontrolled pipe 19 commu- L -p nicating with the outer end of the pipe18 mayA be directed into the furnace. It will of course be understoodthat the particular form and construction of the burner is a matter ofchoice so long as, it is capable of fulfilling the requisite i functionof selectively directing the desired fuel into the furnace, preferablywith an admixture of air aspirated through the burner body from outsidethe furnace.

At its end remote from the furnace each of the checker chambers 5 and 6is preferably connected with a common manifold 22 as shown in Fig. l,and this manifold is in turn connected with a stack 23, a stack damper24 being desirably arranged to control the draft through the stack and,in accordance with the usual practice, a valve 25 of suitable type isinterposed between each of the checker chambers 5 and the manifold and asimilar valve 26 between it and each of the chambers 6 to facilitateproper distribution of the air and spent gases between the severalchambers.

A pair of reversing valves 28, 28 are disposed on opposite sides of thestack connection and are operable to cut oi the ilow of gases to thestack from one side of the manifold or the other and thus enable thefurnace to be reversed, while for supplying air under a suitablepressure to the manifold and from thence to the checker chambers and thefurnace, a fan or blower F of suitable type and capacity is connected toa Y- shaped conduit 29 whose branches respectively communicate with themanifold on opposite sides of the reversing valves 28, 28', saidcommunication being controlled by valves 30, 30 of any suitableconstruction.

The use of a fan, blower or other suitable means Y for supplying airunder pressure to the manifold,

CII

checker chambers and furnace I regard as desirable in the practice ofthe present invention for not only is the volume of air therebyincreased over that which would' be drawn through the chambers bythenatural stack draft, but the resistance to the entrance of the air tothe hearth is also overcome so that the air passes thereto with greatervelocity than it would in the absence of the fan. However, under certainconditions it may be found possible to dispense with the use of the fanand to rely solely upon the natural draft created by 'the stack.

In Fig. 1 the furnace is shown with the several valves in the positionswhich they respectively normally occupy when the furnace is being firedfrom the left-hand end when viewed as in the drawings, and it will thusbe noted that the air from the blower F can pass into the manifoldthrough the valve 30 which is open and from thence into the left-handchecker chambers 5 and 6 through the valves 25, 26 which are also open,the closure of the valve 28 of course preventing any of the air frompassing to the stack. From the checker chambers the heated air passesinto the common slag pocket 9 through the separate necks 7 and 8,upwardly through the uptakes l0, 10 and thence forwardly and downwardlytoward the hearth so as to meet the incoming fuel from the burnersomewhat in advance of the inner end thereof and at such point initiatescombustion. At the opposite or out-end of the furnace, the spent gasespass downwardly through the uptakes 10, l0, thence through the adjacentchecker chambers 5 and 6 and into the manifold, from which they pass tothe stack through the open valve 28', the valve 30' which is now closedpreventing the spent gases from passing into the conduit 29 as well asthe air from the blower from passing into the manifold from the conduit.While the valves 25, 26 are shown open adjacent both ends of thefurnace, it will be understood that individual adjustment of thesevalves may at any time be effected in accordance with the commonpractice so as to more effectively distribute the air and spent gases inthe checker chambers and insure the former entering the furnace at thehighest possible temperature.

When the furnace is reversed after a suitable period of operation, thepositions of the reversing valves 28, 28 are shifted in the usual way aswell as the positions of the valves 30, 30 so as to direct the air int'othe right-hand end, which is now the in-end, of the furnace and permitthe escape of the spent gases from the opposite left-hand end, now theout-end thereof.

In accordance with my invention as will now be readily understood, thefuel employed for the operation of the furnace during the melting downof the charge consists of coke oven, natural or other suitable gasintroduced to the aspirating burner through the nozzle or pipe 14 and inturn to the furnace by the burner together with a small quantity ofcoldA aspirated air ,which is drawn through the latter, the bulk of theair requisite for combustion, however, being preheated in the checkerchambers and meeting the incoming gaseous mixture in front of the innerend of the burner adjacent the end of the hearth, the ames thusgenerated being of non-luminous character and of a temperaturesufficient to melt the charge in a minimum of time. After the charge hasbeen fully or substantially melted, the supplyof gas is turned off' anda suitable liquid fuel introduced through the burner into the furnacetogether, preferably, with a small amount of aspirated air, the liquidfuel so injected meeting the incoming and preheated air from the uptakes10, 10 in front of the inner end of the burner and burning from thatpoint forward with a radiant luminous ame, the temperature of which asabove explained is maintained at a point low enough to prevent excessivedamage to the refractories of the furnace, until the charge is fullyrened and in condition for tapping.

In open hearth furnace operation, the time usually required to melt andrefine the charge in. say, a 100-ton furnace, that is, the time requiredfrom the beginning of the heat until the metal is in condition to tap,varies from approximately 6 to 1l hours. Under such conditions and Witha charge of average composition, the non-luminous flame initially usedin melting the charge in accordance with the present invention isordinarily employed for approximately 3 to 5 hours and the luminousflame for the remainder of the heat, the particular time at which thechange in the character of the flame is made, either gradually or moreor less abruptly, being largely determined by the temperature of thefurnace refractorics and other factors which, in the usual open hearthpractice, dictate the time at which the temperature of the flame usedfor melting should be reduced to prevent excessive deterioration of thefurnace and which are fully understood and recognized by operators ofopen hearth furnaces.

As heretofore pointed out, the interval from the commencement of theheating of a given charge in an open hearth furnace until the charge isin condition for tapping is divided into two distinct periods or stages,namely, that in which the charge is melted, that is, reduced tosubstantial uidity, herein termed the melt-down period, and that inwhich the melted charge is subjected to further heat treatment, hereintermed the refined period, to remove impurities and properly conditionthe bath for tapping.

Toward the end of this period certain metallurgical treatments are oftenresorted to for the purpose of producing certain kinds or grades ofsteel, but these treatments are distinct from the refinement of themetal itself eifected during the refining period. It has heretofore beenthe usual practice to reduce the temperature of the melting flamesubstantially contemporaneously with the completion of the melt-down andthus at about the middle of the total heating time, but in accordancewith the particular conditions present, including the character of thecharge, condition of the furnace and the like, as well understood in theart, the high temperature melting flame is sometimes employed for aproportionately longer or shorter period. Consequently, in accordancewith the present invention, the change-over from the non-luminousmelting flame to the luminous refining flame is usually madesubstantially contemporaneously with the completion of the melt-downwhen it would ordinarily vbe customary to reduce the temperature, butnot to change the character, of the flame, so that the non-luminous andthe luminous flames are generally respectively used for about flftypercent. of the total heating period under usual operating conditions,though within the scope of the invention the change-over may be made forany particular heat either earlier or later as dictated by localconditions so long as the non-luminous flame is utilized for the majorportion the melt-down period and the luminous flame for the majorportion of the subsequent refining period.

It will of course be understood that the reversals of the furnace areeffected in the usual way without regard to the particular character offlame being employed at the moment when each reversal takes place,while, moreover, when burning tar or other viscous fuel, it is usuallycustomary to preheat the same outside of the furnace by any suitablemeans to reduce it to the desired fluidity and to inject a certainamount of steam, supplied through a valve controlled pipe 19' connectedwith the pipe 18, along with the tar as it passes into the burner, aswill be readily understood by those familiar with the art.

While I have referred herein more particularly to the use of my methodin connection with a furnace arranged for selectively burning coke ovengas and tar or other liquid fuel when and as required, under certaincircumstances it may be desired to utilize producer gas or the likeinstead of coke oven gas during the melting of the charge, in which caseit is only necessary to provide any suitable means for directing thisgas into the furnace through the tunnel or port 13 at the temperature atwhich it is drawn from `the producers, although if desired arrangementsmay be made for preheating the gas before its introduction into thefurnace.

My invention is advantageous not only in the direct reduction of thetime required for reiining the charge which it is capable of effecting,but also in the elimination or substantial elimination of foaming of thecharge during the refining period and which is a source of materialdifficulty in the operation of open hearth furnaces in which coke ovengas is employed as a heating medium during that period. This foamingcauses a delay in the heat and is also destructive of the furnace itselfand particularly of its roof; thus, its elimination or substantialelimination is distinctly desirable, tending as it does to reduction ofproduction costs through speeding up the heat, lessening the wear andtear on the furnace, and facilitating its management and operation.

Moreover, the use of my invention does not effect or require any changein the customary metallurgical operations such, for example, as theaddition of ferro-manganese or the like, necessary for producing adesired grade or kind of steel.

While it has heretofore been customary to utilize a non-luminous flamethroughout the heat treatment of the charge in an open hearth furnace,and while attempts have been made to similarly employ a luminous flamebut without much success because of the tendency of that type of flameto cause localized heating of the cold charge and its inability tosatisfactorily penetrate the loosely piled up scrap, as far as I amaware I am the first to use a non-luminous and a luminous flame atdifferent periods in the heat treatment of the charge, and in view ofthe marked advantages arising therefrom as herein disclosed I considermy invention constitutes a material contribution to the art of openhearth steelmaking. I therefore claim my invention broadly withoutreference to the particular apparatus or type of furnace which may beutilized in the practice thereof and without confining or limiting thepractice of the invention to any particular kind or class of fuels as,Within the scope of the appended claims, any suitable fuels may beemployed in its performance.

Having thus described my invention, I claim and desire to protect byLetters Patent of' the United States:

1. In an open hearth steel process, the step of melting down a charge byusing a flame of low luminosity, and refining with a flame of relativelyhigh luminosity.

2. In an open hearth steel process, the steps of melting down with aflame of relatively low luminosity and refining with a flame ofrelatively high luminosity but with a thermal value substantially lessthan that used during the melting down.

3. In the art of open hearth steel manufacture, that method of furnaceoperation which comprises the use of a substantially non-luminous flamederived from combustion of gaseous fuel for melting the charge and of arelatively luminous flame derived from combustion of liquid fuel forrefining it 4. In the art of open hearth steel manufacture, that methodof furnace operation which comprises the steps of melting the charge bymeans of a substantially non-luminous flame derived from combustion ofgaseous fuel, and thereafter refining the charge by means of a radiantrelatively luminousflame derived from combustion of liquid fuel.

5. In the art of open hearth steel manufacture, that method of furnaceoperation which comprises the steps of melting the charge by means of asubstantially non-luminous flame derived from combustion of gaseous fueland thereafter refining the charge by means of a radiant flame of lesstemperature derived from combustion of liquid fuel.

6. In the art of open hearth steel manufacture, that method of furnaceoperation which comprises the steps of melting the charge of the furnacethrough the medium of a substantially non-luminous high temperatureflame derived from combustion of gaseous fuel, and then refining thecharge through the medium of a luminous radiant ame of relatively lowtemperature derived from combustion of liquid fuel.

7. A method of operating an open hearth furnace which consists oftransmitting heat to the charge during the melting down period ofoperation primarily by the method of heat transmission by convection andsupplying heat to the charge during the remainder of the heat periodprimarily by the transmission of heat by radiation.

8. In the art of open hearth steel manufacture,

that method of furnace operation which cornprises utilizing anon-luminous flame initially to eiect a substantial melting of thecharge and then changing the flame to one of luminous character andcontinuing the heating of the charge for the remainder of the totalheating period by means of such flame until it is in condition to tap.

9. In the art of open hearth steel manufacture, that method of furnaceoperation which comprises the steps of initially melting the charge bymeans of a non-luminous flame until the charge is reduced toasubstantially constant level in the bath, and thereafter refining thecharge by means of a luminous flame for a period approximating thatrequired to melt it to thereby bring it to condition for tapping.

10. L,In the art of open hearth steel manufacture, that method offurnace operation which comprises the steps of initially subjecting thecharge to the action of a non-luminous name until the charge has beenreduced to substantially fluid condition and the refractories of thefurnace approach a destructive temperature, and thereupon changing theflame to one of luminous character and lower temperature and continuingthe heating of the charge therewith until the latter is in condition fortapping.

l1. In the art of open hearth steel manufacture,l that method of furnaceoperation which comprises the steps of initially utilizing a nonluminousflame for heating the charge for a period approximating one-half of theentire heat, then changing the flame to one of luminous character andutilizing such flame for heating the charge during the entire remainderof the heat until it is in condition for tapping.

12. In the art of open hearth steel manufacture, that method of furnaceoperation which comprises the steps of utilizing a non-luminous flamefor melting the charge until it is reduced to substantially iiuidity andthe refractories of the furnace approach a temperature suilicient tocause relatively rapid disintegration, then lowering the ame temperatureto a point insuicient to effect such disintegration and changing the ameto one of more luminous character, and continuing the heating of thecharge with such ame for the remainder of the heating period and untilit is in condition to tap.

FRANK E. LEAHY.

